Poop is big business in Dakar, Senegal. That's because a lot of the homes have septic tanks, which need to be cleaned out regularly. The best way to clean your tank is by hiring a proper truck, which arrives with a vacuum.

The problem is that for years, the guys who drove the poop trucks operated as a cartel, and they squashed competition and kept prices high. So a lot of people turned to a cheaper alternative: Men who clear out septic tanks by hand, with shovels and buckets, and basically bury the poop in the street. It's terrible work and bad for the environment.

Today on the show: How economists got sewage off the streets of Dakar by making poop-truck drivers compete with each other. In other words, by breaking up the poop cartel.